Studies on residual stress and surface topography after pneumatic shot peening using discrete element method–finite element method coupled model

After pneumatic shot peening, compressive residual stress is induced on the surface of the target, which will improve the fatigue life. During the process, surface roughness is also induced, which may reduce the fatigue life. To achieve the optimum compressive residual stress with the smallest surface roughness, the formation mechanism of the residual stress field and the surface topography are revealed. Then, pneumatic shot peening is simulated by using a discrete element method–finite element method coupled model. Based on the effects of four variables (the incident angle θ, the initial shot velocity v₀, the shot radius R) and the mass flow rate r_m on five parameters (the equivalent plastic strain, the equivalent stress, the surface compressive residual stress, the maximum compressive residual stress), the surface roughness is investigated. The results show that it induces a residual elastic–plastic strain after the impact of a single shot, which can form a crater and a hemispherical residual stress field. After the impact of many random shots, scattered craters connect with each other, therewith a rough and continuous surface topography is formed. Scattered residual stress fields couple with each other, and a constant residual stress layer with the compressive residual stress in the surface and the tensile residual stress in the subsurface are formed. All five parameters are determined by the residual elastic–plastic strain, which increases as the augment of the normal impact velocity, the shot mass, and the coverage rate. Along with the increase of θ and r_m, these five parameters firstly increase and then decrease; with the increase of v₀ and R, these five parameters increase. Therefore, reasonable values of θ, v₀, R, and r_m should be chosen to obtain the optimum compressive residual stress with as small surface roughness as possible.